Chronic back problems can cause pain and disability for a large segment of the population. Frequently, the cause of back pain is traceable to diseased disc material between opposing vertebrae. When the disc material is diseased, the opposing vertebrae may be inadequately supported, resulting in persistent pain.
Surgical techniques have been developed to remove the diseased disc material and fuse the joint between opposing vertebral bodies. Arthrodesis of the intervertebral joint can reduce the pain associated with movement of an intervertebral joint having diseased disc material. Generally, fusion techniques involve removal of the diseased disc, distraction, drilling a bore for receiving the implant and inserting the implant between the opposing vertebral bodies.
Spinal fusion implants and related surgical instruments for implanting a fusion device are known and disclosed in, for example, U.S. Pat. Nos. 5,741,253; 5,658,337; 5,609,636; 5,505,732; 5,489,308; 5,489,307; 5,484,437; 5,458,638; 5,055,104; 5,026,373; 5,015,247; 4,961,740 and 4,501,269. The disclosure of each of these patents are incorporated herein by reference. Procedures for fusing an intervertebral joint space typically include placement of at least two cylindrical implants in parallel arrangement between the opposing vertebrae.
Some presently available systems for intervertebral fusion provide for preparing an implant site through a hollow tube. Procedures for preparing an implant site through a hollow tube are shown in, for example, U.S. Pat. Nos. 5,484,437; 5,489,307 and 5,505,732. The disclosure of each of these patents are incorporated herein by reference. In some procedures, the implants are also inserted into the prepared site through the hollow tube. Preparing the implant site by passing instruments through a hollow tube advantageously provides for an isolated surgical field with reduced chance of injury to soft tissues surrounding the surgical site.
However, generally, several steps are required for appropriate placement of the implants using present hollow tube systems. These steps include inserting a spacer into the disc space to distract one side of the intervertebral space, then inserting a second spacer for distracting the second side of the vertebral space, followed by placement of the hollow tube over or through a guiding mechanism to orient the longitudinal axis of the implant site relative to the vertebral column. Once the hollow tube is secured in proper alignment, reamers, bores, taps, or other instruments are passed through the hollow tube to prepare the implant site. Either before or after the implant is inserted into the first site, the hollow tube is removed and the procedure is repeated on the opposite side.
Present procedures for placement of an implant through a hollow tube help to reduce the chance of iatrogenic tissue trauma caused by the implant procedure. However, while known procedures provide for reduced chance of injury, the surgeon's accuracy in the relative placement of the hollow tube between the first and second sides is still a matter of guess work and repeated verification using fluoroscopy or radiographic monitoring is needed. Also, the need for individual placement of the hollow guide tube using such methods (i.e., one placement for each implant site) increases the possibility for relative misalignment of the implants to occur during insertion.
One system for decreasing the likelihood of relative misalignment of adjacent implants has been through the use instrument guides comprising dual lumens in fixed relationship to one another. Examples of such instruments are disclosed in U.S. Pat. Nos. 5,055,104; 5,484,437 and 5,797,909. Additional multi-lumen instrument guide systems are disclosed in co-pending U.S. Ser. Nos. 09/081,240 and 09/116,747 which are assigned to Sulzer Spine-Tech Inc., the assignee of the present invention. The disclosure of each of these patents and patent applications are incorporated herein by reference.
However due to the anatomical location of the spinal cord traversing the posterior aspect of the vertebral bodies, presently available dual-lumen guide systems are unsuitable for spinal implant procedures performed from the posterior aspect of the patient's body.
Thus, there is a need for the precision, safety and ease of placement of spinal fusion implants provided by a dual-lumen guide system when the procedure is performed from the posterior aspect of the patient. The present invention is directed to addressing this need.